Theft or sharing?

Noticed this morning that one of the SPN caps I posted on Twitter was posted on Instagram without any credit to me. My first, gut reaction was anger. "How dare they!" But then I thought, "Well, it's just a cap, right? Not like it's fanart or anything." Then I felt more flattered than angry.

But should I be more upset about this sort of thing? In the past I certainly have been. Maybe time has mellowed me a bit? Maybe I shouldn't get upset over my caps being reposted without credit. I mean I do share them with everyone so they can use and enjoy them.